In accordance to the enforcement of manufacturer liability law, higher safeties are now essential to various modern electronic devices. In this tendency, demands for the resistor with fuse function as vital electronic components securing the safety is now increasing.
Among the various conventional resistors with fuse function, a cylindrical resistor and a chip type resistor are now explained referring the attached drawings.
FIG. 6 shows a cross-sectional view of conventional cylinder type resistor with fuse function wherein 1 is a metal film deposited on cylinder shaped alumina insulator 2, 3 is a glass layer having a low melting point deposited on metal film 1, 4 are metal caps establishing electrical connections to metal film 1, 5 are lead wires establishing electrical connections to metal caps 4, and 6 is a protection film covering at least metal film 1 and glass layer 3.
FIG. 7 shows a cross-sectional view of conventional chip type resistor with a fuse function wherein 11 is a metal film deposited on alumina insulator 12, 13 is an upper electrode deposited on the side surface of alumina insulator 12 establishing an electrical connection to metal film 11, 14 is a glass layer having a low melting point deposited on metal film 11, 18 is a protection film covering at least metal film 11 and glass layer 14, and 15 is a side electrode deposited on the side of alumina insulator 12 establishing an electrical connection to upper electrode 13. This side electrode 15 is coated with nickel layer 16 and solder layer 17.
With the above-shown resistor constructions, a fused condition of the conventional resistor can be obtained as shown in FIG. 8. In this case, when metal films 1 and 11 are heated by reactive heat and when the temperature rise caused by this heat reaches to the melting point of the glass layers 3 and 14 each having a low melting point, the glass layers 3 and 14 are melted and the molten low melting point glass is diffused into metal films 1 and 11 loosing the path of electrical conduction. However, due to the deviations of heated condition in metal films 1 and 11, heat capacities or coat thickness of glass layers 3 and 14, diffusion velocity of metal films 1 and 11 into glass layers 3 and 14, thicknesses of metal films 1 and 11, deviations of desired fusing times by the over-load application would be inevitable.
The purpose of the present invention is to solve the above-shown problems and to minimize the deviations of desired fusing time by offering a resistor composition realizing the higher safety of circuit design and the resistors of the same.